The last frontier where mankind can explore, utilize and eventually colonize is outer space. The deciding factor that will determine how fast and to what extent the United States will advance into and develop this new frontier ultimately depends upon how expensive it is to get there. The reusable ground to orbit shuttle vehicle represents a considerable advance toward developing an economical space transportation system. Before this system was developed, the launch vehicles were expendable. Consequently, the cost of transporting passengers and/or bulk cargo to Earth orbit and beyond with those first generation launch vehicles was enormous. The economical impact of using reusable launch vehicles, such as the U.S. Space Shuttle, represented a fundamental breakthrough in reducing the cost of transporting payloads to Earth orbit.
Although designs are currently being advanced to develop more economical reusable ground to orbit space shuttles, there is one fundamental problem that appears to be insolvable. This problem can be called the "initial mass problem" and is inherent in all space vehicles propelled by chemical rocket engines. This problem can best be described by considering the well known "rocket equation" (1). EQU M.sub.1 /M.sub.2 =exp (.DELTA.V/c) (1)
In this equation M.sub.1 and M.sub.2 represent a rocket vehicle's total mass before and after burning its engine to achieve a velocity change denoted by .DELTA.V. The engine's exhaust velocity is denoted by c. The ratio of initial mass to final mass represented by M.sub.1 /M.sub.2 is called the "mass ratio". Thus, the amount of fuel M.sub.f required to achieve a velocity change .DELTA.V is given by M.sub.f =M.sub.1 -M.sub.2. The initial mass M.sub.1 can be calculated by multiplying the mass ratio by the vehicle's final mass M.sub.2. Consequently, in order to keep the vehicle's initial mass M.sub.1 (and required fuel load M.sub.f) as low as possible, the mass ratio should be kept as low as possible. For any given .DELTA.V, it follows from equation (1) that the mass ratio can be reduced only by increasing the exhaust velocity c. Unfortunately, chemical rocket engines have a definite upper limit on c that cannot be exceeded because of fundamental thermodynamics. This upper limit is about 4.50 km/sec. Since the minimum .DELTA.V required to reach low Earth orbit when aerodynamic drag and gravity losses are taken into consideration is about 9.00 km/sec the lowest possible mass ratio corresponding to this .DELTA.V for single stage launch vehicles is 7.39.
In order to illustrate the effect of the initial mass problem suppose that the final "dry mass" M.sub.2 of a single stage ground to orbit chemically propelled launch vehicle is 100,000 kg. Since the minimum mass ratio required to achieve Earth orbit is 7.39, the minimum required initial mass M.sub.1 would have to be 739,000 kg and the required fuel load would be 639,000 kg. Construction experience has shown that the minimum structural mass required for a cryogenic fuel tank is about 10% of the maximum fuel load. Thus, the mass of the fuel tank alone would be about 63,900 kg. This only leaves about 36,100 kg for the remaining structural mass of the vehicle including the payload. These calculations clearly illustrate that it requires a truly enormous launch vehicle, with an enormous fuel load, to orbit even a relatively low mass payload. (The initial mass of the U.S. Space Shuttle is over 2,222,000 kg but the maximum payload is only 30,000 kg.) This is the initial mass problem inherent in all rocket vehicles propelled by chemical rocket engines. Of course, staging does alleviate this problem but when completely reusable launch vehicle designs are contemplated, staging does not offer any significant advantage in terms of reducing overall operational costs. (The U.S. Space Shuttle is considered to be a one and one-half stage vehicle.)
Engineers have studied the initial mass problem for many decades. Since the crux of the problem involves the inherently low exhaust velocities of chemical rocket engines, attempts have been made to develop entirely new engines. But the problem is not simply to develop an engine capable of generating higher exhaust velocities. The engines suitable for launch vehicles must be capable of generating very high thrust to mass ratios. For example, the total thrust developed by a launch vehicle that is launched in the conventional vertical attitude must obviously be greater than the total initial weight of the vehicle if it is to climb off the launch pad.
Ion engines have very high exhaust velocities but have absolute upper bounds on their thrust to mass ratios which are small fractions of unity. Thus, they are totally unsuitable for launch vehicles. Nuclear rocket engines are capable of generating fairly high thrust to mass ratios but the danger of accidentally spraying a highly radioactive exhaust stream over large portions of the Earth's surface render such engines totally impractical. Actually, the nuclear reactors required for these high power engines have inherently high dead inertial mass so that their overall performance is quite limited. But even if there were no possibility of accidents, such engines used aboard manned vehicles would require large amounts of radiation shielding to protect the passengers. This would substantially increase the vehicle's dead inertial mass. Thus, nuclear propelled launch vehicles for manned space travel really do not offer any significant performance advantage.
Other, more exotic rocket engines, have been proposed such as microwave and laser propelled rocket engines. In these engines, a high power microwave or laser beam is directed at the launch vehicle which is captured and focused onto a suitable working fluid such as hydrogen. The working fluid is thereby heated to very high temperatures and expelled out of a conventional rocket nozzle with exhaust velocities significantly higher than those obtainable with chemical rocket engines. (See for example, the papers: "Microwave Rocket Concept," International Astronautical Congress, Vol. 16, Athens, 1965, pp. 175-199 by J. L. Schad and J. J. Moriarty; and "NASA's Laser Propulsion Project," Astronautics & Aeronautics, Sept. 1982, pp. 66-73 by L. W. Jones and D. R. Keefer.) Unfortunately, all of these attempts at circumventing the initial mass problem have failed by a wide margin. Thus, it is now believed that single stage, reusable shuttle vehicles propelled by chemical rocket engines will be the most economical transportation system for launching manned vehicles to low Earth orbit (See, "The Future Space Transportation Systems Study," Astronautics & Aeronautics, June 1983.)
If chemical rocket engines are to be used in any extensive ground-to-orbit space transportation system, there is another important problem to be considered besides the initial mass problem. This problem concerns environmental pollution. If the only practical method available for leaving the Earth's surface on journeys into outer space is at the expense of discharging thousands tons of combustion products into the biosphere, the ability of the biosphere to absorb this pollution will eventually set an upper limit on the rate at which mankind can travel there.
Although microwave and laser propelled launch vehicles were found to be technically impractical for launching manned space vehicles, they had one common and very important characteristic: the energy generating mechanism used to accelerate the vehicle is located off the vehicle. Thus, the amount of energy that can be used to accelerate the vehicle is unlimited. Moreover, since the energy generating source is physically removed from the vehicle, the vehicle is not burdened by having to accelerate its inertial mass. In principle, the combination of these two operating characteristics has the potential of giving a "telepropelled" vehicle very high performance. Unfortunately, the underlying physical principle used to accelerate these microwave and laser propelled launch vehicles was still based upon Newton's third law of motion and therefore stil required the expulsion of large quantities of heated exhaust gases through a rocket nozzle at very high velocity. Thus, in this respect, the microwave and laser propelled launch vehicles were still classical rocket propelled vehicles. Although these vehicles were no longer burdened by having to carry the energy generating source, they were still burdened by having to carry a substantial fuel load for the rocket engines. The underlying physical principle used to generate vehicle thrust was still based on Newton's third law of motion.
The manned Earth to orbit transportation system disclosed herein differs fundamentally from all those of the prior art in that the vehicle thrust forces are not generated by expelling exhaust gases at high velocity out of an exhaust nozzle and applying Newton's third law of motion. Rather, it is based on the principle of electromagnetic propulsion. It, therefore, represents the ultimate and final step in designing the most powerful and economical method for propelling launch vehicles--the complete removal of not only the energy generating source from the vehicle, but also the thrust generating source as well, thereby enabling the thrust forces propelling the vehicle to be essentially unlimited without having to expel any reactive mass whatsoever. Thus, the initial mass problem and the pollution problem are both completely circumvented while enabling the vehicle performance to be virtually unlimited.
In the prior art of Earth to orbit transportation systems it was long recognized that if the required payloads were relatively small and on the order of 100 kg and if there were essentially no acceleration limits that could be exerted on them, the launching system could be a relatively simple catapult whereby the required orbital velocities are reached before the payload leaves the catapult. Since an ordinary gun or cannon is essentially a device for accelerating bodies to very high velocities, it was pointed out over two centuries ago by Isaac Newton in his Principia that a cannon could, in principle, be used as a catapult to launch an object into Earth orbit. A cannon accelerator could obviously be reusable and would therefore represent a very economical means for transporting small payloads to Earth orbit. (See for example, the article "Shells Into Orbit," Machine Design, Jan. 7, 1965, pp. 115-117.) It is interesting to note that this cannon fired launching method was also used by Jules Verne in his famous novel, From the Earth to the Moon. Verne's travelers were placed inside a hollow projectile, and then fired toward the moon at seven miles a second from the mouth of a huge cannon. Unfortunately, the human passengers would have never survived the enormous acceleration loads.
There is another catapult method that can be used to accelerate bodies to high velocities. This method involves the use of magnetic forces. The basic principle was recognized over 100 years ago by Michael Faraday. These accelerators have become known by various names, the most popular of which are: "electromagnetic guns," "electromagnetic launchers," and "mass drivers." Various types of electromagnetic accelerators have been built, tested and patented since the early 1900s. (See, "An Electrical Runway," The Engineer, Vol. 182, Oct. 25, 1946, pp. 379-370; "Theory of an Electromagnetic Mass Accelerator for Achieving Hypervelocities," Langley Research Center, June 1961 by K. Thom and J. Norwood; and "Magnetic Levitation and Propulsion, 1975," IEEE Transactions on Magnetics, Vol. MAG-11, July 1975, pp. 981-995.)
Recently published papers appearing in the literature propose using electromagnetic accelerators for catapulting low mass projectiles directly from the Earth's surface into orbit and beyond. (See, for example, "Electromagnetic Railgun Launchers: Direct Launch Feasibility," AIAA Journal, Vol. 20, No. 7, 1982, pp. 978-985 by R. S. Hawke et al; and "Ablation and Deceleration of Mass Driver-Launched Projectiles for Space Disposal of Nuclear Wastes," AIAA Paper No. 81-0355, AIAA 19th Aerospace Sciences Meeting, St. Louis, Mo. Jan. 12-15, 1981 by C. Park and S. W. Bowen.)
All of the prior art electromagnetic accelerators designed for launching payloads directly into Earth orbit have one common characteristic--very high acceleration. Thus, the payloads are inherently small and are, in fact, called "projectiles". When one contemplates using electromagnetic accelerators for catapulting manned space vehicles directly into orbit from the Earth's surface, the technical problems appear to be insurmountable. Consequently, when such launching systems are described in various publications, the publications are usually science fiction. The main reason for this situation involves acceleration.
One of the major considerations involved in the design of manned launch vehicles is acceleration. If ordinary human passengers are to have access to outer space, the acceleration loads should not exceed approximately 6g's. If this constraint were placed on the design of electromagnetic accelerators, the required length would be enormous. This length can be determined by the well known equation EQU V=.sqroot.2as (2)
that gives the terminal velocity V of a body moving with uniform acceleration a over distance s. Hence, by substituting V=9000 m/sec and a=6g=58.8 m/sec.sup.2, it follows that s=V.sup.2 /(2a)=689 km. Constructing a perfectly straight electromagnetic accelerator this long on the Earth's surface is impossible because of the Earth's curvature. A tunnel would have to be excavated deep underground to a depth of about 8,500 m (27,887 ft.). Unfortunately, it is completely impossible to excavate a large diameter tunnel underground to this depth utilizing prior art tunneling machines or methods.
However, there are other problem that appears to be fundamentally impossible to circumvent. Since atmospheric drag would prevent the accelerator from accelerating a vehicle beyond a certain velocity (well below 9 km/sec) if the vehicle were exposed to the open atmosphere, the entire accelerator would have to be completely enclosed within a giant vacuum tube over 689 km long with a pressure not exceeding 10.sup.-6 torr. This introduces two new fundamental problems that have no solutions in the prior art. It is physically impossible to create a vacuum of 10.sup.-6 torr by mechanical pumping. A vacuum this high (which is equivalent to that found in large space simulation chambers) can only be created with very exotic pumps such as "diffusion pumps" or "cryogenic pumps". These pumps are very large relative to the volume evacuated, they require long pumping times (that can be several days for large chambers) and consume large amounts of energy. Thus, the possibility of achieving a vacuum of 10.sup.-6 torr inside a tube with a diameter of several meters and a length exceeding 689 km mounted inside an underground tunnel is a practical impossibility. Furthermore, even if such a vacuum could be created inside the tube, there would still be the problem of designing a vacuum seal for the end of the tube that would allow a vehicle moving at 9 km/sec to pass through it, into the outside atmosphere, without being destroyed in the process.
When large electromagnetic accelerators for space transportation are described in the scientific literature, they are usually sited on other celestial bodies without atmospheres such as the Moon where atmospheric drag is zero. See, "Electromagnetic Mass Drivers," Progress in Astronautics and Aeronautics, Vol. 57, 1977, pp. 37-61 by F. Chilton et al. and "the Colonization of Space,"
Physics Today, Vol. 27, Sept. 1974, pp. 32-40 by G. O'Neill. The "impossiblity" of launching manned vehicles directly into Earth orbit by an electromagnetic catapult was pointed out by Arthur C. Clarke in his publication "Electromagnetic Launching As A Major Contribution To Space-Flight," Journal of the British Interplanetary Society, Vol. 9, No. 6, Nov. 1950, pp. 261-267.
Prior art electromagnetic accelerators solve the problem of atmospheric drag by sealing off the end of the accelerator tube with a thin diaphragm and evacuating the entire tube prior to actual launch. The projectile breaks through the diaphragm at the end of each launch and, unfortunately, the air reenters the tube destroying the vacuum. A new diaphragm is mounted across the end of the tube and the tube is re-evacuated before the next launch. (See, for example, "Electro Magnetic Propulsion Alternatives," paper presented at the 1979 Princeton Symposium on Space Manufacturing, Princeton, N.J., May 1979 by H. Kolm et al.) Since the diameters and lengths of prior art electromagnetic accelerators are only a few centimeters and a few meters respectively, this solution is quite satisfactory. But the vacuum tube of an electromagnetic accelerator designed to launch manned vehicles would have to have an overall diameter of at least 6 m. The atmospheric pressure acting on a diaphragm with this diameter would be about 644,232 lbs. or 322 tons! In order to support this load, the physical mass of the "diaphragm" would have to be at least 100 kg. Such a mass would completely destroy a vehicle striking it at orbital velocities.
Finally, even it were possible to evacuate a large diameter tube with a length of hundreds of kilometers to a pressure not exceeding 10.sup.-6 torr equipped with a vacuum seal mounted on the end that allows a vehicle to pass through it, into the outside atmosphere with a velocity of 9 km/sec without being destroyed, there would still remain the most difficult problem of all, the thermal barrier. Since the accelerator is several hundred kilometers long, the vehicle would be forced to enter the atmosphere with a very low climb angle that is almost tangent to the Earth's surface. For example, if the accelerator is 689 km long, the climb angle would only be about 3.degree.. Consequently, the vehicle would be catapulted out the end of the accelerator at a relatively low altitude, with a climb angle of only 3.degree., and plung directly into the dense lower levels of the atmosphere at 9 km/sec. Thus, the vehicle would be rammed into a 35,000.degree. K "thermal barrier" at hypervelocity that would cause it to disintegrate long before it could climb out of the atmosphere.
Since each of these problems are considered to be fundamentally insurmountable in their own right, the possibility of catapulting a manned space vehicle from the surface of the Earth directly into orbit solely by means of an electromagnetic accelerator is believed to be a physical impossibility--not a near term impossibility, but an impossibility for the distant future as well.
However, I believe that I have developed practical solutions for each of these problems that are well within current engineering feasibility. I have brought these solutions together to construct not only an electromagnetic accelerator for launching manned space vehicles directly into orbit, but a comprehensive, reusable, electromagnetically propelled space transportation system capable of providing direct transportation between the Earth's surface, the Moon, and even interplanetary space. Moreover, the system is designed such that all of the electrical energy used to operate the accelerator is supplied free of charge by utilizing the very object that all launch vehicles are designed to overcome--the Earth's gravitational field. In fact, the proposed system was invented as a result of viewing the Earth's gravitational field as a powerful ally, rather than as a harsh enemy that must be conquered by applying the traditional brute force techniques of building more powerful rocket engines for propelling more massive launch vehicles. By adopting this underlying design methodology, nature herself can give mankind essentially unlimited launch capability for leaving the Earth's surface and traveling into the new frontier of outer space on an unprecedented scale, on a scale previously believed to be possible only in the realm of science fiction.